Clearance compensation elements are sufficiently well-known in the art and are installed, for instance, in valve drives of internal combustion engines for compensating an undesired increase or decrease in clearance caused by thermal expansion or wear during the operation of the internal combustion engine. These elements operate with a servo means such as a hydraulic medium which is pressed through a leak gap between a housing and a pressure piston during a high pressure phase of the clearance compensation element.
One working in the field knows from the prior art that, especially during the time the engine is warming up from very low temperatures, a compensation, particularly of a decrease in clearance is not accomplished. This decrease in clearance results from the fact that when the engine is started in a cold state, a large heat input takes place, particularly at the exhaust valve and this causes a relative lengthening of the valve with respect to the surrounding components. After several rotations of the cam, hitherto known clearance compensation elements are not able to sufficiently compensate for this decrease in clearance with their leak gap and sink characteristics. This is the case when a gradient of relative sink lengths between the pressure piston and the housing, which cumulate at every successive lift cycle during a temperature variation in the valve drive, is flatter than a gradient of decrease in distance between a base circle of the cam and an end of a valve shaft associated to the clearance compensation element.
The valves, which as a consequence remain open, lead in the extreme case to a failure of combustion by reason of a poor cylinder filling and combustion. Under the most unfavorable conditions, the engine can "die". In addition, unburnt gases also lead to a premature failure of the catalytic converter. Under certain circumstances, once the engine has failed, it is not easy to start it for some time because the valves are still open and compression, as a result, is insufficient. These problems of decrease in clearance are enhanced, among other things, by a too high or pulsating oil pressure.